You need to check and update the VST-paths in Options-dialogue. On a 64 bit system the 32-bit plugins are in a folder with addition (x86), which your 32-bit-rooted  projects most likely don't know.. 

I can't find VST-paths or Options-dialog.
I found a VST tab under Options-global but the "Scan VST folders" and "Reset all VST plug-ins" buttons are not highlighted so they don't do anything when I click on them.
 
This is the message I get when I load projects from the old hard drive  :
 
The following plug-ins are referred to by this project, but could not be found.
They may be missing or improperly installed on your system.
 
The original plug-in state is saved by stand-in plugins, and will be restored if you save the project and subsequently load it on a system where the plug-ins are properly installed.
 
Warning: If you loaded this file in "safe mode", overwriting this file will result in the permanent loss of these effects.
 

Try going through Plugin Manager, and choose the files to be scanned for VSTs. Perhaps that frees the buttons in Options, too?

What you are experiencing is the move from 32 to 64 bit OS. I'm not clear on if there was a 64 bit version of Sonar7, I know 8.5 comes with both.
If this is so then best to install the 32 Bit version , You can have both version installed but make sure you re name the desktop icon cause there's no way to tell. them apart. 
That is why I still have Sonar 7 32 bit installed on my W7 64 bit main DAW. All my old XP 32 bit CWP files load up fine if I need to. 
 
But those VST's can all be found in the Cakewalk sub folders. What I do is copy/paste so they are all in my shared vst folder. All of them. If I find a dll. in any other folders ( Stienberg etc) I copy/ paste to that one folder of my main Sonar. I have 4 Calkwalks in C drive. Copy/paste leaves the original where it belongs so as not to mess up other audio apps. 
Sonar 7 32, Sonar 8.5 32 Sonar 8.5 64 ( main DAW) and Sonar X1 64 which is dormant being the demo which $$ would activate I presume. 
 

Cactus Music
...I'm not clear on if there was a 64 bit version of Sonar7, I know 8.5 comes with both.
If this is so then best to install the 32 Bit version...

Yes, there was a 64-bit version of Sonar 7, but the OP said in Post#10 that he installed the 32-bit version.

The default path for VSTs is:
 
c:\program files (x86)\vst

Sorry it's taken so long to respond to this thread
I've been busy lately but I really appreciate the responses.
 
Kalle,  I don't know how to scan them because they are not in the list of registered plug-ins.
Do they need to be registered somehow?
 
Cactus,  I have the 32 bit version installed on Windows 7 64 bit.
All of my plug-ins are in a folder called Steinberg which is on my D drive.
Which folder am I supposed to paste them into?
 
Kev999, The path for my plugins is -  D:\ Program Files\Steinberg
Sonar is on my C drive.
 
The thing I don't understand is why do all of my audio and MIDI files load from the D drive but the plugins don't?
 
Any ideas welcomed.
Thanks

One New
...I don't know how to scan them because they are not in the list of registered plug-ins.
Do they need to be registered somehow?

...The path for my plugins is - D:\ Program Files\Steinberg... 

Plugins found in the scanning process become "registered".
 
In Plugin Manager, click the Options button to see the filepaths that will be scanned. If "D:\ Program Files\Steinberg" is the only one listed, then your missing plugins must be located elsewhere. Find out where they are and add the appropriate path(s) to this list, then run the scan again.

You need to make Plugin Manager scan the folders where you have installed the VSTs in question.
(Or...I do not remember if Plugin Manager in vs.7 works differently, I don't think it does).
 
Your MIDI files are in the actual project folder, and audio files in the audio folder. The paths to those are exactly the same
as in your previous setup, aren't they? So SONAR finds them. Your 32 bit VSTs are located in a new location, so SONAR has to know where they are in order to use them.
 
It's been a long time since I took a thorough look at the Options , not to mention SONAR 7, but IIRC there really is a window with all the different paths used by SONAR.
 
You have not mentioned which VSTs you're talking about, so I can't say whether they need to be registered or not. If you have
been using them this far, I don't think registration is the culprit here. If a registration is required but not done yet, you do get a nag screen and/or the VST works only in demo mode or doesn't work at all.

There are no VSTs listed in the plugin manager. 
The scan VST folders button is not highlighted so I can't click on it.

 
DXs are listed though.
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I added the steinberg folder under global options but the scan VST folders button is not highlighted so I can't click on it either.